Conventionally, as the light source in liquid crystal display, it is the CCFL (cold cathode fluorescent lamp) which has been used most frequently. The light-emitting principle of the CCFL is identical to that of fluorescent lamps commonly used in offices and households. As shown in FIG. 10, ultraviolet rays are discharged due to occurrence of a chemical reaction of vaporized mercury (Hg+) and electrons (e−) existing inside the lamp, and these ultraviolet rays are perceived as light through the fluorescent material that coats the inside of the lamp. The mercury inside the lamp forms an alloy with metallic material scattered by the electrodes, becoming a mercury alloy (amalgam) of low vapor pressure, and a film of this alloy is produced on the electrodes and fluorescent material inside the lamp. When the mercury in the lamp has turned entirely into alloy, a state is reached where luminance has completely ceased—this point in time constitutes the life of the lamp.
As conventional art, a color-TV door phone apparatus is known which enables the luminance of a cold cathode fluorescent lamp to be stably controlled immediately after activation by controlling the current that flows to the lamp based on the temperature of the cold cathode fluorescent lamp (see, e.g., Patent document 1 (FIG. 3)).    [Patent document 1] Japanese Unexamined Patent Application, First Publication No. 2001-169273